gems, corundum, synthetic corundum.7, flux ruby

Single crystals of corundum were grown by seeded techniques, such as stationary, seed-rotation, and top-seeded, from molten Na- or Li-cryolite (Na₃AlF₆ or Li₃AlF₆) flux. Inclusions—such as flux inclusions, negative crystals, and cavities—present in the crystals were examined under an optical microscope, and the formation mechanisms and shapes of these inclusions, depending on differences in growth technique and conditions, are briefly described.